This invention relates to the hydrogenation of polymers formed by the polymerization of dienes. More specifically, the present invention relates to the use of a fixed bed heterogeneous hydrogenation catalyst to hydrogenate low molecular weight polydienes which may contain functional groups such as hydroxyls.
The polymerization of dienes such as butadiene or isoprene yields polymeric products which are unsaturated. This remaining olefinic unsaturation provides for a mode of polymer degradation from ultraviolet light, ozone or heat. The stability of the polymeric products is greatly enhanced if the olefinic unsaturation is removed by hydrogenation. Dispersed hydrogenation catalysts such as the nickel catalysts formed by the action of an alkyl aluminum on nickel compounds work well to hydrogenate these polymers. Removal of the metal residues from the polymer mixture after hydrogenation by washing the polymer with an aqueous solution of acid can be difficult and costly due to the emulsification of the polymer mixture with the aqueous acid. This difficulty in separation can be even more pronounced if the polymer chain link is relatively short (molecular weight less than about 10,000, and/or if the polymer has functional groups such as hydroxyls.
I have found that a fixed bed catalyst may be used to catalyze the hydrogenation of such short length polymers. This has the advantage of avoiding the need for the difficult and sometimes impossible process steps required to remove catalyst residues from the hydrogenated polymer.